1. Field of the Invention
The present invention relates to a method of manufacturing well-aligned nanotubes and a method of manufacturing a sensor structure using the nanotubes, and more particularly, to a method of manufacturing uniform and vertically-aligned nanotubes by using an organic template, a method of manufacturing a sensor structure having an excellent detection performance at a low cost at the room temperature by simply forming electrodes on upper and lower portions of the nanotubes, and a sensor manufactured by the method.
2. Description of the Related Art
Solid state gas sensors have been widely used to monitor environments or to control chemical engineering processes. Among various solid state sensors, much research has been made to a sensor using a semiconductor metal oxide due to small size, low production cost, and simple manufacturing processes thereof.
FIGS. 1A and 1B are schematic views showing a principle of operation of a gas sensor using a semiconductor metal oxide. As shown in FIG. 1A, when the metal oxide is exposed to air, oxygen gas is adsorbed to a surface of the metal oxide. The adsorbed oxygen is reduced with electrons received from the metal oxide. In the process, a density of electrons on the surface of the metal oxide is lowered, so that resistance is increased. On the other hand, as shown in FIG. 1B, when a reducing gas such as ethanol is introduced, the electrons that are coupled with the adsorbed oxygen molecules are transferred to the metal oxide due to the reaction between the absorbed oxygen molecules and the ethanol molecules. Accordingly, the conductivity of the surface of the metal oxide is increased, and the resistance is decreased.
During the electron exchange process according to the gas introduction, the change in the resistance of the metal oxide is measured, so that the gas can be detected. This is the principle of operation of the sensor using the metal oxide.
On the other hand, in the manufacturing of the gas sensor using the metal oxide, the metal oxide has been formed as a thin film to be used for the gas sensor. However, since the metal oxide has a small surface area per unit volume, the sensitivity of the sensor is not high.
Therefore, much attention has been paid to one-dimensional nano structures, which have a large surface area per unit volume. Accordingly, various nano structures such as nano particles, nano wires, nano bars, and nanotubes have been used for the sensors. Among the nano structures, nanotube structures being vertically aligned with small wall thickness and large surface area are considered to be the best structure.
On the other hand, various methods such as a hydrothermal method, a chemical vapor deposition method, an electrochemistry method, and a template method have been known as a method of manufacturing the nanotube structure. Among the methods, the template method has been widely used due to its advantage capable of easily manufacturing uniform nanotube structure. In the template method, a template having a predetermined shape is formed, and the template is filled with a material, so that a desired structure can be obtained. An AAO (anodic aluminum oxide) and a track-etched membrane are mainly used as the template.
In the process of manufacturing the nanotubes by using the AAO or track-etched membrane template, a wet etching method is used to remove the template. At this time, as shown in FIG. 3A, there is a problem in that the nanotube structure is collapsed or agglomerated. Therefore, the performance of the sensor deteriorates.